Subirrigation System Performance and Evaluation in the Red River Valley of the North

Abstract. Subirrigation (SI) applies water below the ground surface and raises the phreatic water to within or near the root zone by using a subsurface drainage system. It is relatively new to the Red River Valley (RRV) of the North in eastern North Dakota (ND) and west central Minnesota (MN). In 2011, two SI field sites in the RRV were installed and have shown promising results in optimal water management and increasing agricultural production. Unlike a surface irrigation system, SI supplies water below the ground surface over a long duration, water loss is generally through crop transpiration, and leads to negligible water loss via wind, surface runoff and evaporation. Therefore, a new method was developed to evaluate the SI system performance. Water application efficiency (E_a+ET) was calculated through the soil moisture changes in the root zone before and after the SI application plus the evapotranspiration (ET) with known amounts of SI, rainfall, and ET. Uniformity coefficient (UC) and distribution efficiency of low quarter (DULQ) were estimated from the total depth of water stored in the root zone. The SI system performance in 2014 and 2015 showed that the E_a was over 100% for the MN and ND 2014 site-years and 79% for the ND 2015 site-year. The E_a values were high, indicating that the SI system either performed better than typical surface irrigation systems with minimal water loss, or had measurement errors, such as inaccurate ET estimation or excluding the upward flux from the deeper soil. We may have to reformulate how E_a is calculated. The UCs and DULQs were lower than a typical sprinkler and surface irrigation systems, possibly due to its unique SI flow path. Overall, the evaluation indicated that a SI system is effective as a water supply, but the uniformity needs to be improved with a longer SI duration or smaller flow rate.